Parameters of Dicofol Spray Deposit in Relation to Mortality of European Red Mite

Dicofol WP suspensions of 2, 8, and 32 g/liter, deposited as droplets of precisely controlled diameter on discs cut from mature peach leaves, were counted, bioassayed with adult female Panonychus ulmi (Koch), and assayed chemically for dicofol. Within the desired mortality range, 80–95%, the optimum deposit was expressed in a region bounded by the following parameters: droplet diameter of 100 μ with a concentration of 32 g/liter, diameter of 250μ with a concentration of 8 g/liter, deposits of 0.6 and 1.4 μg (γ)/cm2, and droplet numbers of 80 and 250/cm2. With droplets under 200 μ and 2 or 8 g/liter dicofol, no increase in efficacy was obtained by increasing spatial density. Above 1.4 γ/cm2, any advantage gained by using fewer droplets was nullified by wastage of chemical.